Human eyesight is a product of two separate processes that work together to form images for a person to “see.” One of these processes, herein referred to as the physical component, concerns the physical structure of the various elements of the eye and how incoming light is manipulated and processed by the eye. Defects in the shape of the cornea, the retinal wall, or the optic nerve can impair or destroy the functionality of a person's eye and thus impair or eliminate the ability to perceive images. Fortunately, defects in the cornea of a person can be corrected through the use of glasses, contacts, or surgery such as laser keratotomy. Likewise, defects in the retina of a person are often repairable by surgery.
The second process involved in allowing humans to see images is herein referred to as the neurological component. This component concerns neural processing in the brain and how the brain analyzes information sent from the eyes to produce an image. A person can likewise have a number of defects in this component of the visual process, such as reduced visual acuity, reduced sensitivity for spatial contrast, reduced vernier acuity, spatial distortion, abnormal spatial interactions and impaired contour detection.
The physical component and the neurological component work together to form images that a person sees, or more precisely, that a person perceives. The term “perceives” is preferred because, although the physical component may capture certain details, defects in the neurological component may distort and destroy these details, therefore, the image that is “seen” by the person may not be exactly what is captured by the eyes. Consequently, the image that is perceived may differ in detail from the image that is seen by the eyes. Thus, the overall process of human eyesight is herein referred to as the visual perception process.
Defects in the neurological component of a person's visual perception process cannot be remedied through the use of corrective lenses or surgery. Therefore, alternate techniques must be employed to alleviate or correct visual defects in the neurological component of a person's visual perception process.
For example, a common defect in the neurological component of the visual perception process is a condition known as amblyopia. This is a perception defect where the brain incorrectly interprets and processes visual information it receives from the eyes, despite the fact that the physical structure of the eyes may be unimpaired. When addressing amblyopia in children, one approach to correcting defects in the neurological component is to occlude the non-amblyopic, dominant eye and “force” the brain to make greater use of the amblyopic eye. This approach generally strengthens the amblyopic eye and increases its visual acuity. But a significant shortcoming of this approach is that this method is typically only useful in children under the age of nine, and beyond that age the method generally provides insignificant results. Furthermore, occlusion of the non-amblyopic eye is accomplished through the use of an unsightly eye patch, and this often results in social and emotional problems for children. The eye patch may cause skin irritation, as well.
Amblyopic observers suffer from many or all of the neurological defects mentioned above, such as reduced visual acuity, reduced sensitivity for spatial contrast, reduced vernier acuity, spatial distortion, abnormal spatial interactions and impaired contour detection. Amblyopes may also have abnormally high degrees of intrinsic noise, which may form the basis of their abnormal contrast sensitivity function.